A sundew (Drosera species) is a carnivorous plant that uses a sticky mucilage, secreted from specialized tentacles, to trap and digest small insects. The glistening, dew-like appearance of this adhesive attracts prey. The plant absorbs the insects to supplement the nitrogen and phosphorus it cannot obtain from its native, nutrient-poor bog environment. The absence of this sticky “dew” signals that the plant’s immediate environment is not meeting its highly specific requirements.
The Critical Role of Light and Humidity
The most frequent reason a sundew stops producing mucilage is insufficient energy reserves, which are directly tied to light intensity. Sundews require far more light than typical houseplants to fuel mucilage production. Most species need a minimum of four to six hours of direct sun exposure daily, and many thrive under intense lighting for 12 to 16 hours.
If growing indoors, a sunny windowsill is often not bright enough, leading to pale, elongated growth and a lack of dew. Growers should utilize strong artificial lighting, such as high-output LED or fluorescent fixtures, positioned close to the plant. These lights should deliver an intensity of 15,000 to 25,000 lux. Proper lighting allows the plant to produce the necessary sugars for growth, often resulting in a healthy reddish coloration and abundant sticky drops on the new growth.
Air moisture is the second major factor, as the sticky mucilage is largely water-based and highly susceptible to evaporation. If the surrounding air is too dry, the plant will conserve water and the small droplets will evaporate before they can accumulate on the tentacle tips. Many Drosera species prefer a relative humidity level between 40 and 70% to maintain their traps.
To address low air moisture, increase the local humidity around the plant. Placing the pot on a humidity tray filled with water and pebbles, ensuring the pot base remains above the water level, can help. Alternatively, a small, nearby room humidifier can raise the ambient moisture content, allowing the plant to sustain the visible, glistening traps.
Contamination: Water and Potting Medium
Sundews evolved in nutrient-poor environments where the water is naturally pure and acidic, making them extremely sensitive to dissolved solids. Using standard tap water, which contains minerals like calcium and chlorine, is a form of slow poisoning for the plant. These minerals are absorbed by the roots and accumulate in the plant’s tissues and potting medium over time, eventually interfering with the plant’s ability to absorb water and produce mucilage.
Only pure water sources should be used for sundews, specifically distilled water, reverse osmosis (RO) water, or collected rainwater. The concentration of total dissolved solids (TDS) in the water should be 50 parts per million (ppm) or less to prevent mineral buildup and eventual root burn. Sundews are typically grown using the tray method, where the pot sits in a saucer of water, ensuring the soil remains constantly saturated.
The potting medium itself must also be nutrient-free and acidic to mimic the plant’s natural bog habitat. Standard commercial potting soil or garden soil is fatal because it contains fertilizers and minerals that overwhelm the plant’s sensitive root system. The recommended planting substrate is an inert, acidic mix, usually composed of fertilizer-free sphagnum peat moss combined with a drainage material like perlite or horticultural sand, often in a 1:1 ratio.
Natural Dormancy and Environmental Shock
A loss of stickiness can sometimes be a sign of a natural, seasonal cycle rather than improper care, particularly in temperate Drosera species. These varieties, which are native to regions with cold winters, will enter a period of dormancy when daylight hours shorten and temperatures drop in the fall. This resting phase is a survival mechanism where the plant’s active, carnivorous leaves die back.
During dormancy, the plant stops producing dew and forms a tight, non-carnivorous bud of leaves called a hibernaculum at the soil surface. This process is triggered by a combination of a shorter photoperiod and cooler temperatures, and it is a necessary rest period that allows the plant to survive the winter and resume vigorous growth in the spring. Subtropical species, such as the widely available Cape sundew (Drosera capensis), do not typically require this dormancy period and should remain active year-round.
The sudden cessation of dew production can also be a temporary reaction to environmental shock following a move or change in growing conditions. Even if the new conditions are ultimately better for the plant, the sudden shift in light intensity, temperature, or air movement requires an adjustment period. It is common for the plant to halt mucilage secretion for several days or even a couple of weeks while its internal systems acclimate to the new environment.